CT Basement Systems Radon Blog by Matthew A. Bednarz V.P.

News for Homebuyers Regarding Radon Resistant New Construction

Posted by Matthew Bednarz on Fri, Jun, 19, 2015 @ 16:06 PM


Home Buyers: Know What to Ask For

Basic Radon-Resistant New Construction Techniques for Your Home

Based on a rash of recent poorly engineered prefab radon system experiences, I felt it necessary to rehash an old post.  All of the techniques and materials described below are commonly used in home construction.  While the techniques may vary for different house foundations and building site requirements, the five basic features that should included in new construction to prevent radon from entering the home are:

cutaway of house with mitigation system
NOTE: If code allows; alternatives such as a soil gas collection mat can be a viable option.  
  1. Plastic Sheeting or Vapor Barrier / Retarder: Place heavy duty plastic sheeting (6 mil. polyethylene) or a vapor retarder on top of the gravel to prevent the soil gases from entering the house. The sheeting also keeps the concrete from clogging the gravel layer when the slab is poured.             

  2. A Vent Pipe: Run a 3-inch or 4-inch solid PVC pipe, vertically from the gravel layer (stubbed up when the slab is poured) through the house’s conditioned space and roof to safely vent radon and other soil gases outside above the house.  Whenever possible - 4" pipe is a better choice as it allows for up to double the volume of air to be removed out from under the slab as compared to 3".                                                        

  3. For very large footprints, multiple vertical stacks are recommended.  We did a project in a Greenwich estate that had 6 stacks. (Although serving a different purpose, this vent pipe is similar to the drain waste vent, DWV, installed by the plumber for the sanitary system.) This pipe should be labeled "Radon System."       

  4. Sealing and Caulking: Seal all openings, cracks, and crevices in the concrete foundation floor (including the slab perimeter; floor wall joint) and walls with polyurethane caulk to prevent radon and other soil gases from entering the home.                

  5. Junction Box:  An electrical outlet should be provided near the pipe location in the attic.  This is allows for easy fan connection in the event the system has to be activated to effectively reduce radon concentrations.

Some common mistakes made with radon resistant construction pipe installation are;
  • inaccessible attic locations (pipe located where no one can fit),
  • slab stubs located at opposite end of basement from ceiling stub (results in excessive pipe runs),  
  • multiple slab level layouts not being addressed.
Homes located in areas that have water wells should have a second or independent stack installed from the basement ceiling as close to the well tank as possible, to the attic floor.  In the event the water is found to have elevated radon levels, an aeration system will need to be installed.  This system requires a separate exhaust stack.


Topics: radon resistant construction, radon mitigation, radon in air, radon mitigation system, radon testing, radon in air concentrations, indoor radon in air levels, Radon Air, radon mitigation fan, radon concentrations

Radon Resistant New Construction

Posted by Matthew Bednarz on Mon, Jul, 30, 2012 @ 16:07 PM

Radon Resistant New Construction (edit/delete)

Radon Mitigation

Radon resistant new construction is becoming an accepted process by more & more home builders.  There is much misinformation in the marketplace regarding radon...especially regarding new homes.  A common misconception is; radon doesn't exist in new construction.

 Age of a structure can sometimes play a role in determining whether or not there will be a radon problem...but most often, it is not a critical factor. Theoretically; older structures that have substantial air leakage should have lower indoor airborne radon concentrations than newer energy efficient homes. The natural ventilation rate of a leaky home helps dilute down radon concentrations. However, if the radon source is strong enough - even a "leaky" or "energy inefficient" home will still have a radon problem.

It is not possible to completely eliminate radon from entering a new structure.  However; during the early stages of construction - there are radon resistant building practices that can be taken to help "build radon out"...& keep radon concentrations lower than if nothing were done.

 Before the slab is poured, a network of perforated pipe is laid out across the future slab area of the new structure.  There are many pipe configuration variations that can be utilized.  The pic below illustrates a new school we did where the architect required prefab suction boxes with vapor barrier laid under & over the gravel bed.  Whichever pipe configuration is chosen; a stub is connected somewhere in line of this sub slab pipe run.  This stub will be the connection point for a future active radon system if needed.  It is best to try to keep the stub location as close as possible to the intended future vertical pipe run. The new basement floor or slab is poured over the barrier. The new slab is allowed to cure. After curing, any expansion joints, cracks, & the floor wall joint should be sealed with a urethane caulk.

sub slab pipe network

 Once framing has been completed, pipe is connected to the stub that is protruding from the slab, & is routed up through the framed structure, & roof. It is preferable to run the pipe up through the structure in an interior wall to maximize convection . The more streamline the pipe run - the more air that is able to be pulled out from under the slab.  the pipe should penetrate the roof sheathing before the new shingle is installed.

 The other important aspect to keep in mind is where the pipe enters the attic. It will hopefully be located in an area that will remain accessible even after duct work & air handlers have been installed. This becomes key if a radon mitigation fan unit is to be connected to the pipe. Also, there should be 3 feet of vertical / accessible pipe available in the attic to allow for a fan installation if needed.


Interior Route ASD System Interior Route ASD System

After the structure is "conditioned"...it should be tested for radon...this is true even if other new homes in the same area were found not to have a problem.  If a problem is found; a sealed fan can be connected to the pipe in the attic which will create a very effective negative pressure field under the new slab that will prevent soil gas & radon from permeating upward. The active system will also contribute to reducing moisture levels in the basement. The system will be effective & inconspicuous.

 If the home has a private water well, remember to run a second pipe to the attic from a location as close to where the well tank will be positioned in the basement as possible. If a high waterborne radon level is found, an aeration system will be needed to mitigate the radon in water problem.  This system also requires a vent to the exterior. That secondary pipe can be utilized as an exhaust for a future aeration system.  If no problem is detected...the pipe makes for a convenient wire chase.

Radon resistant new construction practices are an important tool for the modern homebuilder.  Aside from preventing radon entry; these procedures ultimately provide a higher degree of comfort - both psychologically & physically - for the new home owner.  Dampness control, better aesthetics, greater reduction efficiencies are all byproducts of a well executed radon resistant construction strategy. There's simply no need to have exposed pipe on the outside of new structures if some forethought is put into design. 

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Topics: ventilation rate, negative pressure, radon resistant construction, well tank, radon, waterborne radon, airborne radon, soil gas, radon mitigation fan, radon fan